1. Field of the Invention
The invention relates to a transformation system for converting visual images into acoustical representations.
2. Description of the Related Art
An article of L. Kay in IEE Proceedings, Vol. 131, No. 7, September 1984, pp 559-576, reviews several mobility aids for totally blind or severely visually handicapped persons. With some of these aids visual information is converted into acoustical representations, e.g. the laser cane, but the conveyed amount of visual information is very low. In fact, these systems are mainly electronic analogs or extensions of the ordinary (long) cane, as they are obstacle detectors for a single direction pointed at. Direct stimulation of the visual cortex has also been tried, but up to now only with poor success. The disadvantage of having to apply brain surgery is an obvious obstacle in the development of this approach. Another possibility is to display an image by a matrix of tactile stimulators, using vibrotactile or electrocutaneous stimulation. The poor resolution of present modest-sized matrices may be a major reason for a lack of success in mobility.
Another approach mentioned in the Kay article is to concert acoustical representations. With this approach, called sonar, the problem of ambiguity arises, because very different configurations of obstacles may conceivably yield almost the same acoustic patterns. Another problem is that the complexity of an acoustic refraction pattern is very hard to interpret and requires extensive training. Here too the spatial resolution is rather low due to a far from optimal exploitation of available bandwidth. The range of sight is rather restricted in general. The document WO 02/00395 (which corresponds to U.S. Pat. No. 4,378,569) discloses a system in which an image sensed by a video signal generator is converted into sound information through a number of circuit channels corresponding with the number of pixels in a line of the image. This results in bulky circuitry mismatches in which may cause inaccuracies in the sound information generated.